A representative digital power distribution system using PET protocol is described in U.S. Pat. No. 8,781,637 filed in 2012 (Eaves 2012). The primary discerning factor in a digital power transmission system compared to traditional, analog power systems is that the electrical energy is separated into discrete units, and individual units of energy can be associated with analog and/or digital information that can be used for the purposes of optimizing safety, efficiency, resiliency, control or routing.
In apparatus described in Eaves 2012, a source controller and a load controller are connected by power transmission lines. The source controller of Eaves 2012 periodically isolates (disconnects) the power transmission lines from the power source and analyzes, at a minimum, the voltage characteristics present at the source controller terminals directly before and after the lines are isolated. The time period when the power lines are isolated was referred to in Eaves 2012 as the “sample period,” and the time period when the source is connected is referred to as the “transfer period”. The rate of rise and decay of the voltage on the lines before, during and after the sample period reveal if a fault condition is present in or across the power transmission lines. Measurable faults include, but are not limited to, short circuit, high line resistance or the presence of an individual who has improperly come in contact with the lines. Since the energy in a PET system is transferred as discrete quantities, or quanta, it can be referred to as “digital power”.
A representative digital power distribution system, as originally described in Eaves 2012, is shown in FIG. 1. The system is comprised of a source 1 and at least one load 2. The source 1 is an analog power source, meaning that the electrical power is delivered in a continuously variable format, as is the standard worldwide in today's analog power distribution systems. For example, 120 VAC, 60 HZ is an analog power distribution system format.
The PET protocol is initiated by operating the switch 3 via the source controller 11 to periodically disconnect the source 1 from the power transmission lines via an on/off signal 20. The combination of a switch 3 and the source controller 11 can be collectively referred to as a transmitter 16.
When the switch 3 is in an open (non-conducting) state, the power transmission lines are also isolated from any stored energy that may reside at the load 2 by an isolation diode 4. A load-side capacitor 5 is representative of an energy storage element on the load side of the circuit. The power transmission lines have inherent line-to-line resistance and capacitance, respectively represented by transmission-line resistor 6 and transmission-line capacitor 7. The PET system architecture, as described in Eaves 2012, can insert additional line-to-line resistance (via an additional resistor 8) and capacitance (via an additional capacitor 9). The combination of the isolation diode 4, load-side capacitor 5, and additional capacitor 9 can be collectively referred to as a receiver 12.
At the instant when the switch 3 is opened, the transmission-line capacitor 7 and the additional capacitor 9 have stored charge that decays at a rate that is inversely proportional to the additive values of resistances provided by the transmission-line resistor 6 and the additional resistor 8. The load-side capacitor 5 does not discharge through the additional resistor 8 or through the transmission-line resistor 6 due to the reverse blocking action of the isolation diode 4. The amount of charge contained in the transmission-line capacitor 7 and the additional capacitor 9 is proportional to the voltage across them. The voltage can be measured at point 10 by the source controller 11 via a voltage signal 21 communicated from point 10 to the source controller 11.
As described in Eaves 2012, a change in the rate of decay of the energy stored in the transmission line capacitor 7 and in the additional capacitor 9 can indicate that there is a cross-line fault on the transmission lines. The difference between normal operation and a fault, as presented by Eaves 2012 is illustrated by the plot of voltage over time shown in FIG. 2, where the voltage drop, ΔV, during normal operation (as shown in the first sample period) can be seen to be significantly less than the voltage drop, ΔV, with the cross-line fault (as shown in the second sample period).